This invention relates to an arrangement for protecting journal bearings of the fan drive systems for turbofan engines by preventing undesired rotation and supplying oil to the journal bearings during rotation.
Turbofan engines include fan sections driven by planetary gear systems. Journal bearings in the systems reduce friction between planetary gears and corresponding support shafts. An oil system supplies oil to lubricate each of the journal bearings. An oil pump maintains pressure within the oil system to ensure each of the journal bearings receives an adequate supply of oil.
Turbofan engines may be used to propel a multi-engine aircraft. In such an aircraft, one of the turbofan engines may shut-down during flight if a fault condition occurs. The oil pump also shuts down when the turbofan engine is not operating. Although the turbofan engine is shut down, airflow through the moving engine may continue to rotate (i.e., windmill) the fan section of the turbofan engine. Without some oil supply, the journal bearings may seize and harm the turbofan engine or prevent operation of the turbofan engine. Preventing windmilling while the aircraft is in the air causes drag as the stationary fan section impedes airflow through the turbofan engine.
When the aircraft is on the ground, airflow through the turbofan engine may cause the fan section to windmill. Without some oil supply while windmilling, the journal bearings may seize and harm the turbofan engine.
Accordingly, it is desirable to provide an arrangement for lubricating journal bearings when the fan section is windmilling during flight, and to prevent the fan section from windmilling when an aircraft is not in flight.